Video sender

A video sender (also known as a DigiSender, wireless video sender, AV sender or audio-video sender) is a device for transmitting domestic audio and video signals wirelessly from one location to another. It is most commonly used for sending the output of a source device, such as a satellite TV decoder, to a television in another part of a property and provides an alternative to cable installations.

A wide range of video sender technologies exist including wireless (radio), spread-spectrum, power-line communication and WiFi. Other, less common technologies also exist, such as those that utilise existing ethernet networks.

Typical applications include the transmission of Television audio and video signals from a lounge to a bedroom, from a CCTV camera to a monitor or television and interconnecting appliances with Audio and Video as well as IP (Internet Protocol) requirements.

Some video senders also incorporate a return path, to permit infrared remote controls to operate the equipment whose output is being sent. The equipment usually features SCART (Europe), composite video or HDMI as their key means of connection to host equipment. More recently RJ45 connectors for LAN have been added to some models.

Video senders offer analogue or digital solutions and are used to create connectivity around the home without the needs for cabling.

Analogue versions may be subject to RF interference from other household wireless appliances such as cordless telephones or wireless networks and are becoming increasingly unpopular but retain a significant low cost advantage. Where-as digital models utilise standards more familiar with Computer Networks such as Power-line communication or WiFi and are increasingly more popular as they handle HDMI connectivity and some can even pass Internet connectivity through to connected equipment.

Analogue solutions have the advantage of low manufacturing costs as the Video and Audio signals are simply modulated onto a carrier at 2.4 GHz or 5.8 GHz. But they have the adverse effect of causing reduced bandwidth to WiFi networks and in some cases WiFi networks can cause picture interference on the video sender signal. More information can be found in the article on electromagnetic interference at 2.4 GHz. See [1] for explanation and mitigation. To avoid this, some video senders now use a technology similar to WiFi and can co-exist with wireless networks and share available bandwidth.

Usually there are four FM transmit channels, A, B, C & D, with L & R audio on 6.0 MHz and 6.5 MHz FM subcarriers added to the composite video baseband. The reverse remote control channel is usually 433.92 MHz, fixed, using whatever modulation is on the 34 kHz to 45 kHz IR remote "carrier". ASK/OOK schemes such as RC5 and RC6 work best over the RF link as the receiver uses a data slicer and AGC designed for ASK/OOK with Manchester encoding.

Digital solutions are now the most popular and combine the use of a System on Chip (used for picture and sound encoding/decoding) with a means or launching the signal such as Power-line communication, WiFi or Ultra-wideband (also known as UWB, ultra-wide band and ultraband). Ultra-wideband is generally used for low range applications of typically 10 meters maximum where a simple link is required from the source to a monitor or television. Some manufacturers use proprietary versions of Wi-Fi technology enabling greater ranges to be achieved of typically 80 meters in-building and in excess 2 kilometres clear line-of-sight with the use of externally mounted antennas. Some Digital models maintain an advantage of achieving HD or even 4K UHD and provide additional connectivity standards such as HDMI, RJ45 as well as analogue connectivity standards such as SCART (Europe) and composite video.

In 2010 a new standard for cabled applications was released called HDBaseT a consumer electronic (CE) and commercial connectivity technology for transmission of uncompressed high-definition video (HD), audio, power, home networking, Ethernet, USB, and some control signals, over a common category (Cat5e or above) cable with a standard connector (RJ45).

In November 2010, UK company AEI, achieved a 720p wireless link over a 2KM range using their own propitiatory technology operating in the 2.4 GHz - 2.45 GHz ISM band and operating at 100 mW ERP.